Gas plasma display panels have been known for some years and typically comprise a mixture of two or more gases at a suitable gas pressure disposed in a transparent chamber or envelope. An array of electrodes are positioned on both sidewalls of the envelope, and each electrode is normally coated with a layer of dielectric material, which is itself coated with an electron emissive layer. The electrodes are arranged such that the electrodes on one sidewall are positioned substantially perpendicular to those on the other sidewall. The points at which one electrode on one sidewall is juxtaposed an electrode on the opposite sidewall results in a point at which they cross; this is known as the pixel point. During the operation of the plasma panel, an increased voltage pulse is applied to one of the electrodes creating a voltage differential across the gas envelope at a given pixel point. When the voltage is great enough, the gas between these electrodes at this point begins to ionize. The energy level at which this ionization occurs is called the write voltage (V.sub.w).
During the gas ionization process, the gas, located between the pixel point electrodes, is stripped of at least one electron creating free electrons which are drawn to the positive electrode and positively charged gas ions which are drawn to the negatively charged cathode electrode. These free electrons collide with other gas atoms, on their path to the respective electrodes, causing an avalanche of effect of free electrons and ions, this being the plasma. As the positive ions are drawn to the cathode, they strike the emissive layer which coats the dielectric material disposed above the electrode at that pixel point. Upon striking the emissive layer, electrons are removed from the atoms of the emissive layer, some of which combine with the ionized gas forming neutral neon gas atoms and others which are drawn toward the anode. In this way, electrons are removed from the emissive layer creating a localized positive charge thereon. This positive charge is called a wall charge (V.sub.wall). The significance of this wall charge is that at the next half cycle, when the cathode electrode becomes the anode electrode, the wall charge present at the pixel point will be cumulative to that voltage applied to the electrode, thereby lowering the voltage required to again ionize the gas to below that of the initial write voltage. This lower voltage is called the write sustain voltage (V.sub.ws) and is the difference between the wall voltage and the write voltage. This is clearly set out mathematically as EQU V.sub.ws =V.sub.w -V.sub.wall
In the operation of these plasma panels, it is apparent that in order to maintain a low stable, repeatable write sustain voltage, it is desirable to maintain a high wall voltage. Unfortunately, during the generation of the wall charge on the emissive surface, electrons from the dielectric layer, below the cathode surface are electrostatically drawn through the thin cathode emissive surface layer to combine with the positive ions of the emissive layer and replace the diminishing supply of surface electrons. This migration of electrons causes the dielectric layer's surface to become positively charged. This charged surface then starts to spread along the entire surface of the dielectric layer due to charge dispersion forces and the ionic qualities, (i.e. contaminants, etc.) of the dielectric surface. The further away from the original energized pixel intersection site that the charge migrates within a given time period, the less positive charge within the pixel area will be available for the next half cycle when the fields reverse and the cathode becomes the anode. This ever-changing wall charge causes an ever-changing write sustain voltage requirement. In addition, as the charge spreads along the surface of the dielectric layer, it may alter the electrical state of neighboring pixels causing them to ignite prematurely.
Therefore, what is needed in this art, is a means to supply sufficient number of electrons to the emissive cathode surface, yet prevent the positive charge generated due to the loss of these electrons, from spreading along the surface of the dielectric layer. Such a means would lower and maintain the electrical requirements for each pixel to a normal and stable write sustain voltage as well as reduce crosstalk between neighboring pixels.